Craniosynostosis is the pathologic fusion of the sutures of the calvaria. It is associated with significant morbidity, occasional mortality, and carries a considerable financial burden. Using a combination of candidate gene resequencing and comparative genome hybridization TWIST1 loss-of-function mutations and IGF1R and RUNX2 gain-of-function mutations have been identified. Expression array analysis coupled with network modeling has identified activation of an IGF1-RUNX2 pathway as a potential cause of craniosynostosis in a large subgroup of cases. The identification of a biologically based subgroup is a critical advance toward understanding the cause of synostosis as it affords an ability to focus research efforts on a phenotypically similar cohort of cases. This competitive renewal proposes the use of genomics, network modeling, animal models and novel cell biologic approaches to reveal genetic and developmental pathways which, when disrupted, result in premature calvarial fusion. New (Igf1rGOF) and existing (Igf1GOF, Gsk3bLOF, Twist1LOF) mouse resources will be used to model the polygenic inheritance of this disorder. Through interdisciplinary research efforts, three independent yet highly integrated aims will test the hypothesis that a subset of children with isolated single suture craniosynostosis has identifiable genetic variation that results in enhanced calvarial osteoblast differentiation throug activation of an IGF1-RUNX2 pathway. Specific Aim 1 will identify changes in the cellular phenotype of osteoblasts demonstrating activation of the IGF1-RUNX2 pathway. We will utilize measures of osteoblast growth and differentiation as well as measures of cellular biomechanics to refine the biologic phenotype of our original cohort. Specific Aim 2 will develop and characterize an inducible Igf1rR407H mouse model of the human IGF1RR406H gain-of-function mutation.11 We will breed and phenotype Igf1rR407H compound heterozygous mice using existing mutant mouse resources (Igf1GOF, Gsk3bLOF, Twist1LOF) to develop models for the polygenic inheritance of SSC in humans. Specific Aim 3 will determine the contribution of genomic variation in the development of craniosynostosis among cases in the IGF1/RUNX2 subgroup. We will use transcriptome sequence data from the original cohort (N=211) and whole genome sequence data from the IGF1/RUNX2 subgroup cases (N=48) to refine the pathway and identify correlates between alteration in gene expression, coding variants and regulatory region variation. We will recruit a new SSC cohort to validate the transcriptomic and genomic variation identified. Major gaps exist in the diagnosis and management of isolated craniosynostosis including the lack of molecular diagnostic testing, adequate family counseling, and biologic therapies to reduce patient morbidity. There is an incomplete understanding of the causes of craniosynostosis and we lack experimental models. The development of these resources will improve clinical care, design biologically based therapies, and pursue primary prevention.